The United States is in the midst of an opiate addiction crisis, with rates of opiate misuse and abuse estimated to be over 2.5 million, including both licit and illicit opiates. In addition to the devastating consequences to the current population, which include overdose, addiction, lost productivity, socioeconomic burdens, and social and familial deterioration, a growing body of evidence indicates that widespread opiate exposure will also affect subsequent generations. The experiments proposed in this application will examine the mechanisms underlying transmission of this environmental exposure from sires to offspring utilizing a rat model of opiate exposure. Examination of paternal transmission is ideal because the confound of gestational and rearing environment is mitigated as the only contribution from the sire is semen. Semen, and specifically spermatozoa represent a cell type that undergoes vast modifications and regulations including replacement of histones by protamines in the DNA in order to more tightly package the DNA into the head of the sperm and retention of specific histones, small RNA expression including micro RNA and other non-coding RNA molecules, and DNA methylation, erasure, and remethylation. The specific aims of this grant will examine epigenetic modifications to the sperm and the effect that they have on the developing blastocyst. In Aim 1 we will examine the acetylation of histones retained within the sperm and the specific promoters and genes with which they are associated. In Aim 2 we will utilize deep sequencing techniques to measure expression levels of RNA species within the sperm. In Aim 2B we will examine blastocysts for these same RNA species as well as correlate them with mRNA expression changes between blastocysts derived from morphine exposed sires and saline exposed sires. The data that will be produced from the proposed experiments will provide insights into the mechanism of transmission of behavioral phenotypes associated with paternal opioid exposure. In addition, these mechanisms can be expanded more broadly and represent means by which environmental stimuli can impact phenotypic variation of future progeny.